Emitter structure and production method

ABSTRACT

An emitter structure includes a substrate with a membrane arrangement. The membrane arrangement includes at least one first membrane, a first heating path and a second heating path in different substrate planes. The first heating path and the second heating path are positioned with respect to one another such that a projection of the first heating path and a projection of the second heating path onto a common plane lie at least partly next to one another in the common plane.

This application claims the benefit of German Application No.102018201997.5, filed on Feb. 8, 2018, which application is herebyincorporated herein by reference.

TECHNICAL FIELD

Exemplary embodiments relate to an emitter structure comprising amembrane arrangement comprising at least two membranes, and to acorresponding production method. Further exemplary embodiments relate toa non-dispersive infrared sensor system and to a photoacousticspectroscopy system comprising a corresponding emitter structure.

BACKGROUND

Detecting environmental parameters such as noise, sounds, temperaturesor gases, for example, is becoming more and more important in the caseof mobile terminals, domestic automation systems or sensors for theautomotive sector. Gas sensors, in particular, are playing an ever moreimportant part here in order to detect for example harmful gasconcentrations on account of air contamination or malfunctions ofinstallations. In accordance with the general development trend, gasdetectors of this type ought to be able to be produced expediently andto be distinguished by permanent availability and high precision.

NDIR sensor systems (non-dispersive infrared sensor systems) constitutea spectroscopic device for gas detection. This spectroscopic devicetypically comprises a source of infrared radiation, a tube (curvette)containing the gas to be analyzed, radiation being transmitted throughsaid tube, and also an infrared detector (and possibly a wavelengthfilter). The concentration of the gas sought is determined electrooptically on the basis of the absorption of a specific wavelength in theinfrared spectrum. One of the components having the highest influence onthe measurement quality is the infrared radiation source. For the latterit is possible to use infrared lasers, infrared LEDs or thermal MEMSinfrared sources, for example.

SUMMARY

Exemplary embodiments of the present invention provide an emitterstructure comprising a substrate having a membrane arrangement. Themembrane arrangement comprises at least one first membrane, a firstheating path and a second heating path. The two heating paths arearranged in (mutually) different substrate planes, wherein the first andsecond heating path are positioned with respect to one another (e.g. onthe membrane if one membrane is assumed, or a respective membrane if aplurality of membranes are assumed) such that a projection(perpendicular to the substrate) of the first heating path and a(parallel) projection of the second heating path onto a common plane areimaged at least partly next to one another in the common plane. To putit another way that means that the two heating paths are thus positionedsuch that they do not or substantially do not overlap. This has theadvantage that the emitter structure constitutes a heating structure inthe sense of a temperature source in which a (to the greatest possibleextent) homogenous temperature emission profile (e.g. for emittinginfrared radiation) is generated over the emission surface (e.g. thetopmost membrane).

There are two variants for realizing the arrangement of the two heatingpaths at different substrate planes. In accordance with one exemplaryembodiment, the membrane arrangement comprises the first membrane, witha first heating path on a first main surface of the first membrane (e.g.on a top side) and the second heating path on a second main surfaceconfigured opposite the first main surface (i.e. e.g. the underside). Inthis case, it is advantageous if the membrane is thick enough to giverise to a spacing apart of the two heating paths.

In accordance with a second exemplary embodiment, the membranearrangement can comprise a first and a second membrane, each of whichthen accommodates one of the two heating paths. In this case,accommodates means that the heating structure (heating path) are appliedon the top side or the underside or are integrated directly into saidmembrane (integrated in the sense of embedded).

In accordance with exemplary embodiments, the emitter structure can beused as infrared source in an NDIR (non-dispersive infrared sensor)system or in a photoacoustic spectroscopy system for gas detection.Consequently, the exemplary embodiments provide a non-dispersiveinfrared sensor system comprising an infrared sensor element and acorresponding emitter structure, and also a photoacoustic spectroscopysystem comprising an infrared sensor and an emitter structure. Onaccount of the homogenous temperature distribution, a very accuratelycontrollable and homogenous emission of the infrared radiation iseffected, such that the measuring systems produced by means of theemitter structure explained above yield very accurate results. Sincesuch MEMS emitter structures are also able to be produced costeffectively, the systems described combine the advantages of costeffective production and very good metrological properties.

Exemplary embodiments are not restricted to emitter structurescomprising two membranes and two heating paths, such that an emitterstructure having the above arrangement and also a third membrane in themembrane arrangement is provided in accordance with further exemplaryembodiments. The third membrane likewise comprises a third heating path.The third heating path is arranged such that a projection of the thirdheating path onto the common plane lies next to the projection of thesecond heating path and/or next to the projection of the first heatingpath. The homogenous emission characteristic can be optimized further bymeans of the third or each further membrane layer having a heatingelement. Furthermore, it should be noted at this juncture that theheating paths are generally connected in parallel, such that the overallarrangement of the heating elements enables low resistance operation,that is to say is advantageous with regard to the power demand.

In accordance with exemplary embodiments, the projection of the firstheating path relative to the projection of the second heating path canbe spaced apart from one another at least in a region along the firstand the second heating path. Moreover, the projection of the firstheating path and the projection of the second heating path can alsoadjoin and overlap one another at least in a region along the first andthe second heating path. If meander shaped heating paths are assumed,for example, the meander structures always run parallel to one anotherin the projection, such that no overlap arises. However, if ring shapedstructures are assumed, then an overlap of the projection areas of thetwo heating paths can arise at least by virtue of the connection regionof the inner ring. In accordance with exemplary embodiments, the firstand/or the second heating path have/has—depending on the desired purposeof use—a meander shape and a ring shape or else an area shape. Inaccordance with further exemplary embodiments, each heating path isconstituted by a metallization applied on the membrane, a doping or someother resistance element.

As already mentioned above, in accordance with exemplary embodiments, anemission region that emits the infrared radiation is formed by amembrane, in particular the first membrane. When looking at thisemission region, the arrangement explained above makes it possible that,in accordance with exemplary embodiments, a projection area of the firstheating path together with a projection area of the second heating pathforms a larger projection area than each projection area by itself. Byway of example, the projection area can be 1.3 or 1.5 or even 2.0 timesthe magnitude of one of the projection areas alone. Preferably, thecommon projection area forms exactly the sum of the projection area ofthe two heating paths. In accordance with further exemplary embodiments,the membrane arrangement can comprise an additional membrane designedfor the emission. Said additional membrane is configured to distribute athermal energy induced by the first and/or the second heating path overa lateral area of the further membrane and/or accordingly to emit theinfrared radiation. This affords the advantage of further optimizing theemission characteristic.

In accordance with exemplary embodiments, the substrate comprises anopening, such as e.g. an opening produced by means of the Bosch method,or a trench (deep trench), in which the membranes are arranged. In thecase of a trench, the membranes together with the trench form a cavity.The opening or cavity has the advantage that these regions do not serveas a heat sink and the response time and overall the heating capacityare thus improved. In accordance with exemplary embodiments, themembranes are spaced apart from one another, such that an interspace isformed between the membranes. In accordance with further exemplaryembodiments, said interspace can be filled with a gas or fluid, forexample. This filling has the purpose or advantage that the membranesare thermally coupled to one another in order to produce the desiredtemperature profile or temperature pattern on the first membrane(topmost or bottommost membrane). In order, in accordance with exemplaryembodiments, to allow the enclosed gas to escape upon its expansion onaccount of the heating, the first and/or the second membrane cancomprise a ventilation opening. Alternatively, the ventilation openingcan also be provided in the substrate. These ventilation openings havethe advantage of the membrane not being mechanically loaded on accountof thermal expansion and change in volume owing to the heating of theenclosed gas.

In accordance with a further exemplary embodiment, the emitter structurecomprises an integrated ASIC configured to drive the first and thesecond heating path. In this case, by way of example, a DC or ACexcitation can be induced by the ASIC, wherein, by way of example, an ACexcitation in the radio frequency range (e.g. 100 megahertz) enables anoptimization of the temperature profile. In accordance with exemplaryembodiments, the heating elements of the individual membranes can alsobe driven separately from one another in order to vary the temperatureprofile or generally to vary the temperature. In accordance with oneadvantageous variant, the temperature of the neighboring membrane can bedetermined by means of the pattern from the heating path in order thusto carry out the control in a more targeted manner.

A further exemplary embodiment provides a method for producing anemitter structure comprising the central step of forming a membranearrangement in a substrate comprising shaping a first membrane with afirst heating path and shaping a second membrane with a second heatingpath, such that the first and the second membrane are arranged withrespect to one another in such a way that a projection of the firstheating path and a projection of the second heating path onto a commonplane lie at least partly next to one another. In accordance with afurther exemplary embodiment, the method can also be extended by theprevious step of introducing a trench or an opening, wherein the step offorming the membrane arrangement is then carried out such that the firstand/or the second membrane are/is arranged in the opening or the trench.As already indicated above, the method has the advantage that an emitterstructure which offers advantageous measurement properties by comparisonwith other emitter structures produced by means of MEMS technologies canbe produced in a cost effective manner by means of this method.

BRIEF DESCRIPTION OF THE DRAWINGS

Developments are defined in the dependent claims. Exemplary embodimentsare explained with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic illustration of an emitter structure inaccordance with one basic exemplary embodiment;

FIG. 2a shows a schematic sectional illustration of an emitter structurein a substrate with a trench in accordance with one exemplaryembodiment;

FIG. 2b shows a schematic sectional illustration of an emitter structurein a substrate with an opening in accordance with a further exemplaryembodiment;

FIG. 3a-3c show schematic partial views of membranes for illustratingthe arrangement of the heating paths in accordance with exemplaryembodiments;

FIGS. 4a and 4b show diagrams for comparing a resulting temperatureprofile in the case of emitter structures in accordance with exemplaryembodiments;

FIG. 4c shows a further diagram for comparing a resulting temperatureprofile in accordance with exemplary embodiments; and

FIG. 5a-5d show variants of the lateral design of heating paths inemitter structures in accordance with exemplary embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Before exemplary embodiments are explained in detail below withreference to the accompanying drawings, it should be pointed out thatidentically acting elements and structures are provided with identicalreference signs, such that the description thereof is applicable to oneanother or mutually interchangeable.

FIG. 1 shows an emitter structure 10 for emitting heating energy, e.g.infrared radiation. In this exemplary embodiment, the heating energy isemitted for example in the direction of the arrow IR. The emitterstructure 10 illustrated here is illustrated schematically as a threedimensional representation without additional elements such as thesubstrate in which the membrane arrangement is introduced. The emitterstructure 10 comprises a membrane arrangement, such as a membrane stack,for example, which is formed by the two membranes 12 and 14. Thesemembranes 12 and 14 are arranged parallel/substantially parallel and inan overlapping fashion with respect to one another, i.e. at least partlyoverlapping or preferably even congruent. It should be noted at thisjuncture that even if the membranes 12 and 14 are illustrated with aquadrilateral shape, they can, of course, also have a round shape orsome other freeform shape. In accordance with one exemplary embodiment,both membranes 12 and 14 are spaced apart from one another, such that aninterspace 13 is formed therebetween, which interspace can be fillede.g. with a gas (e.g. air) or fluid (generally: electrically insulatingmaterial).

Each of the membranes 12 and 14 comprises a heating element in the formof a heating path 12 a and 14 a, respectively. The first heating path 12a associated with the first membrane 12 extends along an arbitraryshape, such as e.g. the U-shape illustrated here or along a meandershape on or in the associated first membrane 12. Analogously thereto,the second heating path 14 a likewise extends along the surface of theassociated membrane 14 with an arbitrary shape. Both heating paths 12 aand 14 a are shaped from a lateral standpoint such that they arearranged in a non-overlapping fashion, which is explained below withreference to the projection of the two heating paths 12 a and 14 a ontoa common plane GE.

The projection of the heating path 12 a is identified by means of thereference sign 12 a*, while the projection 14 a is identified by thereference 14 a*. The projection is effected perpendicular to themembranes 12 and 14 or perpendicular to the substrate (not illustrated)accommodating the membrane arrangement 12+14 of the emitter structure10. As a result, the projection plane GE thus lies substantiallyparallel to a main surface of the substrate or to the membranes 12 and14. As can be discerned, the projection areas 14 a* and 12 a* extendsubstantially next to one another or, in this exemplary embodiment,completely next to one another. This arrangement next to one another inthe projection onto the common plane GE results because the heatingelements 12 a and 14 are arranged in a manner significantly offset withrespect to one another in order to achieve a temperature distributionthat is as homogenous as possible at the topmost membrane uponactivation of said heating elements, as will also be explained below.

It should be pointed out at this juncture that, in accordance withexemplary embodiments, it suffices for the projections 14 a* and 12 a*to extend next to one another regionally, such that individual smalloverlaps or intersection points of the projections 12 a* and 14 a* wouldbe conceivable, wherein this overlap can originate for example fromcontacting lines. Even if in this exemplary embodiment the illustrationwas such that there is a distance between the projections 14 a* and 12a*, it would, of course, also be possible for said projections todirectly adjoin one another or even partly overlap one another.

Now that the emitter structure 10 has been explained with regard to itsstructure, the functioning will be discussed below.

Each of the heating paths 12 a and 14 a is conductive (e.g. metallizedor doped) and emits a dedicated temperature profile upon excitation witha voltage (DC or AC), said temperature profile in principle followingthe shape of the conductors 12 a and 14 a. By virtue of the fact that,rather than one plane, a plurality of planes with individual heatingpaths 12 a and 14 a are provided and said heating paths also lie in amanner spatially offset with respect to one another, at the emissionsurface of the emitter structure 10, e.g. at the surface of the membrane12, upon emission in the direction IR, a homogenous temperaturedistribution is achieved as a result of superimposition of theindividual temperature distributions. With elements of this type it ispossible to achieve a temperature emission (directly at the element) inthe range of from room temperatures (starting from 20° C.) up to 600° C.

For the purpose of preferred driving in accordance with exemplaryembodiments: the emitter structure 10 or the resulting layer stack 12+14comprising the heating paths 12 a and 14 a forms an arrangement ofresistance and impedance elements, wherein the elements of the differentlayers are preferably connected in parallel, which enables lowresistance driving with a correspondingly low total power. The heatingelements can be configured as resistive elements, for example, such thata temperature increase is brought about by a DC or an AC excitation.Alternatively, a design as an impedance element would also be possible,such that an AC excitation (e.g. in the megahertz range) brings about atemperature emission by means of the impedance element.

Even if, in exemplary embodiments above, it was assumed that themembrane arrangement comprises the membranes 12 and 14, in accordancewith further exemplary embodiments the same concept can also be realizedwith one membrane, e.g. one thick membrane, in the case of which arespective heating structure (heating path 12 a and 14 a) is provided onthe top side and on the underside. This approach of the single membraneas membrane arrangement having different heating structures in differenttopologies is advantageous on account of the simple producability.Furthermore, it should be noted that, in accordance with furtherexemplary embodiments, said single membrane or each membrane can alsocomprise heating structures in the membrane itself, in order to forme.g. a third heating path.

FIG. 2a shows an emitter structure 10′, here comprising 3 or generally nmembranes 12′, 14′ and 16′ (silicon or generally semiconductormembranes) arranged in a trench 22 of the substrate 20 (bulk substrate).A cavity is formed below the bottommost membrane 16′. Each membrane 12′,14′ and 16′ (e.g. polysilicon membrane) comprises heating elements, hereprovided with the reference sign 12 a′. As can be discerned, the heatingelements 12 a′, 14 a′ and 16 a′ are arranged in a manner offset withrespect to one another, i.e. thus the membrane elements 14 a′ betweenthe membrane elements 12 a′ and the membrane element 16 a′ between themembrane elements 14 a′.

A further exemplary embodiment is illustrated in FIG. 2b , which showsthe emitter structure 10″. The latter in turn has the three membranes12′, 14′ and 16′ with the associated heating elements 12 a′, 14 a′ and16 a′, wherein here the membranes 12′, 14′ and 16′ are not arranged in atrench but rather in an opening introduced into the substrate 20 forexample by means of the Bosch process. The opening is provided with thereference sign 24.

As already indicated above, the membranes 12′, 14′ and 16′ arepreferably composed of polysilicon since this material has a highemissivity. As already explained above, the heating elements 12 a′, 14a′ and 16 a′ can be shaped as doped regions in the membranes 12′, 14′and 16′ or else comprise other electrical elements having heatingproperties, i.e. thus having a high power loss in the structure. That isto say therefore in other words that a resistance, of whatever kind, isgenerally used.

In accordance with exemplary embodiments, the membranes 12′, 14′ and 16′can have ventilation openings, identified here with the reference signs12 v′, 14 v′ and 16 v′ (cf. FIG. 2a and FIG. 2b ). Said ventilationopenings connect the interspaces between the membranes 12′, 14′ and 16′to one another and additionally also connect the interspaces to theexterior region, i.e. thus e.g. in a direction toward the emission areaor in the opposite direction toward the cavity 22 or the opening 24. Thepurpose of these ventilation openings 12 v′, 14 v′ and 16 v′ is toenable pressure equalization, in particular excess pressure, by virtueof the fact that the gas volume enclosed between the membranes 12′, 14′and 16′ can escape through the ventilation openings 12 v′, 14 v′ and 16v′ if said gas volume expands on account of the thermal expansion. Afurther advantage afforded by said openings 12 v′, 14 v′ and 16 v′ isthat thermal insulation vis à vis the substrate 22 is improved onaccount of the fact that, by virtue of the ventilation openings 12 v′,14 v′ and 16 v′, the membrane is perforated and as it were the thermalbridge is reduced.

Referring to FIGS. 3a and 3b , an explanation will now be given of howthe geometric design of the heating elements 12 a″ and 14 a″ of theemitter structure 10″ can be configured. In the exemplary embodimentfrom FIGS. 3a and 3b , it is assumed that the first heating element 12a″ and also the second heating element 14 a″ have a ring shape. In thiscase, FIG. 3a illustrates a three dimensional illustration of the twoassociated membranes 12″ and 14″ with the heating elements 12 a″ and 14a″, while FIG. 3b shows a plan view or a frontal view of the projection.

It is evident in the projection illustration, in particular, that bothheating elements 12 a″ and 14 a″ are interleaved in one another in aring shape fashion, although the electrical contactings (cf. 12 k″ and14 k″) are arranged in a manner overlapping one another, with the resultthat a region of contact or overlap region thus arises.

In accordance with exemplary embodiments, this contacting region canalso be arranged in a manner offset with respect to one another in orderto avoid hot spots here on account of the supply of energy. In the caseof such arrangements, the contacting region 12 k″ would then be arrangedat a different position, e.g. in the manner distributed over thecircumference of the membrane 12″/14″, compared with the contactingregion 14 k″.

FIG. 3c shows a sectional illustration through an emitter structure10″′. Since the heating elements 12 a″′ and 14 a″′ and also themembranes 12″′ and 14″′ are rotationally symmetrical, only an excerptaround the rotation axis 12 r, 14 r is illustrated here. In the outerregion, the membranes 12″′ and 14″′ are held by the substrate 20″′.

With regard to the dimensioning, it should be pointed out by way ofexample that it is assumed here that each membrane has a thickness inthe 100 nm range, while the height of the cavity extends over a range ofhundreds of μm. The two membranes are spaced apart a few μm from oneanother, said membranes having a diameter of a few 100 μm. Eachconductor track has approximately a width of a few 10 μm. All theseindications should be understood as value ranges, such that the membranethus has a diameter of 100 to 3000 μm, and the cavity can have a depthof 100 to 1000 μm. Likewise, the thickness of each membrane can vary inthe range of 100 nm to 2000 nm, wherein the distance would then alsovary with the order of magnitude of 1 μm to 5 μm. The chosen diametersof the conductor tracks of the heating elements depend essentially onthe desired impedance and can vary between 5 and 300 μm.

Referring to FIG. 4a , a possible temperature distribution is discussedbelow on the basis of the emitter structure 10″′, wherein it is pointedout that the heating elements 12 a″′ and 14 a″′ are heated at 600° C. Asillustrated, what is advantageously achieved is that the substrate 20has a significantly lower temperature, e.g. room temperature of 25° C.(generally at least 10 times lower).

FIG. 4a illustrates the temperature profile on the basis of only theupper membrane 12″′ with the reference sign T12. As can be discerned,this temperature profile T12 has the maximum M12 in the outer region.The temperature profile resulting from parallel operation of the heatingelements 12 a″′ and 14″′, said temperature profile being illustratedwith the reference sign T14+T12, is significantly increased incomparison with the temperature profile T12, an additional maximumM14+M12 also being obtained. In FIG. 4b , the additional energy gainintroduced by the multi dual membrane 10″′ is identified by means ofhatching (cf. reference sign E12+E14).

FIG. 4c shows the optical energy plotted against the wavelength for ahomogenous heating element (cf. curve having the dots), a standardsingle heating element (cf. line having the strokes) and the optimizedheating element having the two or the plurality of membranes. As can bediscerned, the optical energy at the wavelength λ1 approximates to thehomogenous heating element, such that a significant improvement can beachieved in comparison with the standard heating element.

Referring to FIGS. 5a to 5d , an explanation will now be given ofpatterns in which the heating elements 12 a and/or 14 a from FIG. 1 orelse from the other exemplary embodiments can be arranged.

FIG. 5a shows the emitter structure 10″″ or the plan view of theassociated membranes 12″″ and 14″″. As can be discerned, each membranecomprises a meander shaped heater provided with the reference sign 12a″″ or 14 a″″, respectively. The two meander shaped heaters 12 a″ and 14a″ are offset by 90° with respect to one another, which affords theadvantage of achieving a large area with the resulting emission pattern.Furthermore, the connections are also oriented differently.

FIG. 5b shows an emitter structure 10″″′ comprising the two heatingelements 14 a″″′ and 12 a″″′, wherein both heating elements 12 a″″′ and14 a″″′ are embodied as so called ring meanders. In this case, the ringmeander 14 a″″′ is smaller than the ring meander 12 a″″′ with regard toits diameter. In this case, it should also be mentioned advantageouslythat the two ring meanders 12 a″″′ and 14 a″″′ have their contactingsrespectively on different sides, such that no hot spots can arise hereeither.

FIG. 5c shows an emitter structure 10″″″ comprising two ring shapedelements 12 a″″″ and 14 a″″″′, wherein an enlarged illustration showsthat the heating element itself is formed by a lightly doped region,while the region surrounding the heating element can be constituted by ahighly doped region.

FIG. 5d shows a further exemplary embodiment, wherein two (or possiblymore) heating elements 14 a″″″′ and 14 b″″″′ or respectively 12 a″″″′and 12 b″″″′ are provided per membrane. In this exemplary embodiment itbecomes clear that a plurality of heating elements can be arranged nextto one another per membrane.

It should be noted at this juncture that even if, in exemplaryembodiments above, it was always assumed that the heating track isembodied as a track, planar elements such as heating plates, forexample, can also be provided.

In accordance with a further exemplary embodiment, an additionalemission membrane can additionally be provided on the emission side,i.e. on the membrane 12 for example in the case of the emitter structure10 from FIG. 1. Said additional emission membrane can have higheremission properties in comparison with the membrane 12, which thenadvantageously distribute the emission pattern even more homogenously. Asuitable material for this further (emission) membrane is polysiliconowing to the improved emission properties in comparison with standardsilicon membranes.

Even if, in exemplary embodiments above, it was always assumed thatemission takes place via the membrane 12, nevertheless it is alsopossible for the temperature emission to take place via the lowermembrane.

Referring to the dimensioning of the membranes and the choice of fillingfor the interspaces, it should be noted that these can be used to adaptthe properties of the element (thermal capacity and reaction time). If afluid or a solid is present e.g. in the interspace, the optical reactiontime is reduced since the thermal capacity is also reduced.

Further exemplary embodiments relate to a sensor system (PAS SensorSystem or an NDIR Sensor System) comprising an emitter structure asexplained above. An additional exemplary embodiment relates to aproduction method essentially comprising the steps of arranging themembranes with the heating elements in such a way that the heatingelements do not overlap, i.e. are preferably arranged next to oneanother. Conventional MEMS production technologies such as are used e.g.for microphone production can be used in this production method.

In accordance with a further exemplary embodiment, the structure can beconnected to an ASIC or generally to a controller that can be used toactivate and deactivate or regulate the individual elements. By adaptingthe power per heating element, it is possible to adapt the thermalprofile and thus also the optical emission characteristic/emissionpattern. In this case, it is conceivable, for example, for the differentheating elements to be driven differently in different planes or elsefor a temperature sensor on one plane to be taken as a basis formonitoring the temperature of the heater of the other plane in orderthus to carry out a control.

Although some aspects have been described in association with a device,it goes without saying that these aspects also constitute a descriptionof the corresponding method, and so a block or a component of a deviceshould also be understood as a corresponding method step or as a featureof a method step. Analogously thereto, aspects described in associationwith or as a method step also constitute a description of acorresponding block or detail or feature of a corresponding device. Someor all of the method steps can be performed by a hardware apparatus (orusing a hardware apparatus), such as, for example, a microprocessor, aprogrammable computer or an electronic circuit. In some exemplaryembodiments, some or a plurality of the most important method steps canbe performed by such an apparatus.

1. An emitter structure comprising: a substrate having a membranearrangement comprising at least one first membrane, a first heating pathand a second heating path, wherein the first heating path and the secondheating path are arranged in different substrate planes and arepositioned with respect to one another such that a projection of thefirst heating path and a projection of the second heating path onto acommon plane lie at least partly next to one another in the commonplane.
 2. The emitter structure as claimed in claim 1, wherein themembrane arrangement comprises the first membrane with the first heatingpath on a first main surface of the first membrane and the secondheating path on a second known surface of the first membrane, saidsecond ring surface being situated opposite the first main surface. 3.The emitter structure as claimed in claim 1, wherein the membranearrangement comprises the first membrane with the first heating path anda second membrane with a second heating path, wherein the first membraneand the second membrane are arranged in different substrate planes inorder to arrange the first heating path and the second heating path indifferent substrate planes.
 4. The emitter structure as claimed in claim1, wherein the projection of the first heating path relative to theprojection of the second heating path is spaced apart from one anotherat least in a region along the first and the second heating path.
 5. Theemitter structure as claimed in claim 1, wherein the projection of thefirst heating path and the projection of the second heating path arearranged in a manner adjoining or overlapping one another at least in aregion along the first and the second heating path.
 6. The emitterstructure as claimed in claim 1, wherein the first membrane forms anemission region configured to emit infrared radiation.
 7. The emitterstructure as claimed in claim 1, wherein a projection area of the firstheating path together with a projection area of the second heating pathforms a larger projection area than the projection area of the first orthe second heating path alone.
 8. The emitter structure as claimed inclaim 7, wherein a projection area of the first and the second heatingpath onto the common plane together is 1.3 times, 1.5 times or 2.0 timesthe magnitude of a projection area of the first heating path or aprojection area of the second heating path.
 9. The emitter structure asclaimed in claim 1, wherein the substrate comprises an opening, in whichthe membrane arrangement is arranged.
 10. The emitter structure asclaimed in claim 1, wherein the substrate comprises a trench, in whichthe membrane arrangement is arranged, wherein the second membranetogether with a trench form a cavity.
 11. The emitter structure asclaimed in claim 3, wherein the first membrane and the second membraneare spaced apart from one another, such that an interspace is shapedbetween the first membrane and the second membrane.
 12. The emitterstructure as claimed in claim 11, wherein the interspace is filled witha gas.
 13. The emitter structure as claimed in claim 11, wherein atleast one of the first and the second membrane comprise a ventilationopening, such that a gas volume enclosed in the interspace can escapetoward the outside in the event of its expansion; and/or wherein thesubstrate comprises a ventilation opening for the interspace, such thatan enclosed gas volume can escape toward the outside in the event of itsexpansion.
 14. The emitter structure as claimed in claim 3, wherein theemitter structure comprises a third membrane with a third heating path,wherein the third heating path is arranged relative to at least one ofthe first and the second heating path such that a projection of thethird heating path onto the common plane lies next to the projection ofthe second heating path and/or next to the projection of the firstheating path.
 15. The emitter structure as claimed in claim 1, whereinthe first heating path and/or the second heating path have/has a ringshape; or wherein the first heating path and/or the second heating pathhave/has a meander shape.
 16. The emitter structure as claimed in claim1, wherein the membrane arrangement comprises a further membraneconfigured to distribute a thermal energy induced by the first and/orthe second heating path over a lateral area of the further membrane andto emit infrared radiation.
 17. The emitter structure as claimed inclaim 1, wherein the first and/or the second heating path comprise(s) adoping.
 18. The emitter structure as claimed in claim 1, wherein theemitter structure comprises an ASIC configured to drive the first andthe second heating path.
 19. A non-dispersive infrared sensor systemcomprising an infrared sensor element and an emitter structure asclaimed in claim 1, which is configured to emit an infrared radiation.20. A photoacoustic spectroscopy system for gas detection comprising aninfrared sensor element and an emitter structure as claimed in claim 1,which is configured to emit an infrared radiation.
 21. A method forproducing an emitter structure, the method comprising: forming amembrane arrangement in a substrate comprising at least one firstmembrane, a first heating path and a second heating path, wherein thefirst heating path and the second heating path are arranged in differentsubstrate planes and are positioned with respect to one another suchthat a projection of the first heating path and a projection of thesecond heating path onto a common plane lie at least partly next to oneanother in the common plane.
 22. The method as claimed in claim 21,wherein the method further comprises introducing a trench or an openingbefore forming the membrane arrangement, and wherein the forming themembrane arrangement comprises forming the membrane arrangement arrangedin the opening or the trench.